The present invention relates to the field of optical detectors.
The performance of a semiconductor optical detector is determined by complicated relations between the device design, material parameters, and processing capability. Although many designs are conceived, their implementations are hindered by lack of suitable fabrication procedures. It is desirable to provide for a simple fabrication procedure for producing a Schottky diode optical detector that maximizes conversion from optical power to electrical current without diminishing the response speed. Our new design reduces sources of noise current, maximizes the light sensitive area and employs a fabrication process without performance limiting complications.
InGaAs epitaxially grown on InP is a desirable choice for the light absorbing material, since this material strongly absorbs IR at 1.3 and 1.5 microns, for efficient use in communication applications. Fabrication of Schottky optical signal detectors requires the formation of high quality Schottky barriers providing low dark current and good sensitivity. This is not easily achieved on a low band-gap material such as InGaAs. A barrier-enhancing layer, such as InAlAs improves the Schottky contact, and thus the performance of such devices and thus should be included in the design of the IR optical detector. A fabrication process is desired which provides safety shielding of the sensitive front side Schottky contact, to protect it during further processing upon manufacture. Prior art metal-semiconductor-metal (MSM) detectors employ finger electrodes which block a significant fraction of incident light, decreasing the ultimate sensitivity of the detector. This problem is avoided if the device is illuminated through a transparent substrate or if the substrate is selectively removed. Hence, it is a further goal of the invention to provide a fabrication process for removing the InP substrates, initially required for good epitaxial growth of III-V layers grown thereon. This removal, along with providing transparent front ohmic contacts, simplifies alignment of light input sources illuminating the transparent ohmic contacts, such as optical fibers, to the light sensitive areas of the detector. Removal of the InP substrate also decreases the fraction of reflected radiation, which increases the detectors efficiency.